BibTeX is the bibliography format LaTeX has read since 1985. BibLaTeX is the modern rewrite of BibTeX, with the same .bib extension. pandoc sits between the two, and this page says exactly what happens to a BibTeX file on the way to becoming a BibLaTeX one.
What runs when a BibTeX file becomes BibLaTeX
pandoc 3.1.3, on a machine we rent and watch. Your BibTeX file is uploaded once, pandoc runs once, the BibLaTeX comes back, and neither file is kept. BibTeX to BibLaTeX is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the BibTeX into the BibLaTeX
Every reference, and every field BibLaTeX has a place for. The engine counts the entries on the way in and on the way out and refuses the result if the number moved, because a bibliography that comes back with half its references passes every format check and is still wrong.
Authors in the order you had them, with the family name still separated from the given name. That separation is what lets a citation style print "Durand, M." in one journal and "Marie Durand" in the next, and it is the first thing a naive converter flattens into one string.
Every field you sent, including the ones this writer throws away. We put one entry carrying eleven fields through all three writers and read the output field by field: the pandoc writer for BibLaTeX drops keywords, because BibLaTeX has a field for almost everything, so almost nothing has to be dropped on the way out. KEYWORDS is taken back from the intermediate form and put in, never over what the writer kept.
A key that LATEX actually accepts. This is not a formality: pandoc will happily write `@article{O'Brien_2019,`, and the apostrophe stops `\cite` from resolving. Anything unsafe is rewritten, and a response header says how many.
The DOI, the ISBN, the ISSN and the URL, which is worth saying plainly because the pandoc writer for BibLaTeX drops some of them. They are taken back from the intermediate form and put in, never over what the writer kept.
What BibTeX to BibLaTeX costs you
Nothing measurable. The pandoc BibLaTeX writer drops keywords, and they are put back. Everything else this pair was given comes out the other side.
Nothing you would notice, and the field NAMES change, which is the whole point. BibTeX writes `journal` and `year`; BibLaTeX writes `journaltitle` and `date`. The same reference, said in the vocabulary the other one reads.
Where BibTeX and BibLaTeX files come from
BibTeX. Written by Oren Patashnik for LaTeX, and still the reason every reference manager offers a .bib export. Each entry is a type, a citation key and a list of fields. The key is what \cite{...} looks for, which is why a file whose keys are broken is a file you throw away.
BibLaTeX. A rewrite that moved the work from BibTeX's own language into LaTeX, and renamed the fields on the way: journaltitle for journal, date for year. It shares the .bib extension with BibTeX and is not the same file, which is the whole reason to convert between them.
If a model is going to read the BibLaTeX
A bibliography is a list of claims a model can check rather than prose it has to interpret: each entry names an author, a year, a journal and often a DOI. BibTeX in, BibLaTeX out, with every field the target has room for, which is what lets a model answer "which of these are after 2019" without reading a single abstract.
BibTeX to BibLaTeX, measured rather than promised
Running BibTeX to BibLaTeX against the real engine with a real file, pandoc wrote 394 bytes of BibLaTeX in under a tenth of a second, machine otherwise idle. That is one BibTeX file on one day and not an average, which is why the number is given together with the file that produced it.
The BibTeX to BibLaTeX verdict was reached by counting the references back out and checking every citation key, meaning every reference was counted back out of the output, and every citation key in it was checked for being non-empty, unique, and made only of characters LaTeX accepts in a cite command. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the BibLaTeX file has anything inside it.
What we will not pretend about BibTeX to BibLaTeX
A BibTeX file over 5 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A BibTeX to BibLaTeX run that passes 30 seconds is killed, and the pandoc process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
This does not deduplicate, merge or check anything. Two copies of the same paper come out as two references, a wrong year comes out wrong, and a DOI that points nowhere is carried across unchanged. It converts one bibliography into another shape of the same bibliography.
One BibTeX file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
BibTeX to BibLaTeX: what people ask
What actually converts my BibTeX file to BibLaTeX?
pandoc does it, 3.1.3, on a machine we rent and watch. Not a browser trick and not somebody else service: the BibTeX file is uploaded once, pandoc runs once, the BibLaTeX comes back, and neither file is kept afterwards.
How long does BibTeX to BibLaTeX take?
On the file the probe used, pandoc took under a tenth of a second and wrote 394 bytes of BibLaTeX. That is one real measurement on one real BibTeX file, not an average and not a promise about yours: a larger BibTeX takes longer, and past 30 seconds the run is stopped.
What do I lose going from BibTeX to BibLaTeX?
The one to know about first: Nothing measurable. The pandoc BibLaTeX writer drops keywords, and they are put back. Everything else this pair was given comes out the other side.
Will my citation keys still work?
Yes. A key you wrote yourself is never touched. Only a key that is empty, duplicated, or holds a character LaTeX will not take in a cite command is rewritten, and a response header says how many.
Will the file compile?
That is the thing this page is really about. Most converters hand you the raw pandoc output, which from an EndNote XML contains `@article{,`, an entry with no key at all. It opens in an editor and it does not compile. Every key that comes out of here is non-empty, unique, and made only of characters `\cite` accepts.
Is BibLaTeX not just BibTeX?
They share the .bib extension and they are not the same file. BibLaTeX writes `journaltitle` where BibTeX writes `journal`, and `date` where BibTeX writes `year`, among others. A file written for one is read by the other only as far as the field names happen to agree.
Is BibTeX to BibLaTeX free?
There is a free allowance every month, and one BibTeX to BibLaTeX conversion costs half a credit against it. When the allowance runs out the tool says so and stops, rather than quietly handing you a worse BibLaTeX.